To detect the exact location of an intruder on a particular mat? Can't see the point of that, so I assume your intention is to have many mats each with a single large detection area, and wire these mats in a matrix? If so, listen to the points @TomGeorge Is talking about, they will be significant problems.
An alternative would be to have one small Arduino for each mat and have them communicate to a central Arduino by RF or rs485 or something.